Research ArticleGEOLOGY

Transient glacial incision in the Patagonian Andes from ~6 Ma to present

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Science Advances  12 Feb 2020:
Vol. 6, no. 7, eaay1641
DOI: 10.1126/sciadv.aay1641
  • Fig. 1 Map of study area.

    Study area with the modern exposure of the Patagonian batholith, faults, and sample locations. LBA, Lago Buenos Aires; MLBA, Meseta del LBA; NPI, North Patagonian Icefield; CTJ, Chile Triple Junction; LOFZ, Liquiñe-Ofqui fault zone. Geologic units other than the batholith and the glacial deposits are not shown. The extent of the Guivel and Mercer till exposures is not visible at this scale, as the meters-thick units are intercalated with basalt flows and outcrop in narrow bands that follow the contour of the meseta edge. The four sampling locations are marked by stars. Published bedrock AHe data (single samples or sample suites) are shown by squares (15), circles (20), diamonds (8), and pentagons (16). Large black symbols indicate data that appear in the top of Fig. 3 and in table S1. Small white symbols indicate other published bedrock ages, which are shown for reference but not used for our analysis. Faults in the region are shown in orange (15).

  • Fig. 2 Regional climate record and deposit ages.

    The black curve is the deep-ocean water temperature from an ice volume–corrected model based on the global benthic foraminifera δ18O record (32). The colored rectangles indicate the depositional age constraints on the sampled glacial deposits. The circles indicate intersection of the lowest temperature associated with the depositional age range for each deposit.

  • Fig. 3 AHe lag times for samples in this study.

    Vertical red ticks indicate the lag times of individual cobbles reported here and published modern bedrock samples (8, 15, 20). Blue curves in the bottom four panels are lag time probability density plots (35), as estimated by AHe minimum ages for each cobble. (Top) Solid blue lines represent predicted probability density curves for modern bedrock using Leones and Nef age-elevation relationships (AERs) in (15); dashed blue lines represent predicted probability density curves for modern bedrock using DES and LL AERs in (20) (see Results and Materials and Methods for details; AER locations are shown in Fig. 1). Vertical dashed lines indicate relevant mean values, and black arrows indicate first quartile values for the lag time distributions. The uncertainties are ±2 SE, and the uncertainty for first quartile values is determined numerically using a bootstrap method.

  • Fig. 4 Summary of the evolution of erosion rates in the source region sampled by the AHe cobble ages.

    The black curve shows the evolution of the averaged erosion rate within the source region (fig. S3 shows a larger plot of this curve). The color bars show the fastest rates, as represented by the first quartile value of the erosion rate distribution for each deposit. The horizontal extent of each color bar shows the lag interval (AHe closure to deposition) for each of these “fastest erosion” estimates. The gray curve shows, in schematic fashion, the evolution of the fastest eroding part of the source region. The right-hand axis shows the correspondence between lag time and erosion rate, as determined from the age2edot program (see fig. S6A).

  • Table 1 Mean and first quartile lag time and erosion rates.

    Sample locationDepositional
    age (Ma)
    NMean
    lag ± 2 SE (Ma)
    Mean erosion
    rate ± 2 SE (km/Ma)
    First quartile
    lag ± 2 SE (Ma)
    First quartile
    erosion
    rate ± 2 SE (km/Ma)
    Bedrock515.84 ± 1.80.3335
    (+0.10/−0.08)
    3.50 ± 1.20.5310
    (+0.20/−0.14)
    Fenix I0.0185297.51 ± 2.00.3196
    (+0.10/−0.08)
    4.51 ± 0.920.5255
    (+0.10/−0.12)
    Telken VII1.0162210.09 ± 6.40.2419
    (+0.22/−0.12)
    2.94 ± 0.680.7804
    (+0.16/−0.18)
    Guivel3.3154.80 ± 3.20.4937
    (+0.46/−0.24)
    0.48 ± 0.822.9780
    (+2.0/−12.6)
    Mercer5.7624.23 ± 12.60.0928
    (+0.10/−0.04)
    11.65 ± 8.60.2006
    (+0.08/−0.26)

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/6/7/eaay1641/DC1

    Fig. S1. Example photos of till and moraine deposit morphology.

    Fig. S2. Lag time plot showing all AHe ages (including all replicate ages).

    Fig. S3. Average erosion rate curve from Fig. 4.

    Fig. S4. Color bars showing lag intervals for all AHe cobble ages in our study, plotted separately for each deposit.

    Fig. S5. Simplified version of Fig. 3.

    Fig. S6. Age2edot output.

    Fig. S7. Evolution of the closure depth in response to an instantaneous increase in erosion rate.

    Table S1. Published bedrock ages shown in Fig. 3.

    Table S2. Crystal AHe measurements and ages.

    Data S1. Google Earth file (.kml) of sample names and locations.

  • Supplementary Materials

    The PDF file includes:

    • Fig. S1. Example photos of till and moraine deposit morphology.
    • Fig. S2. Lag time plot showing all AHe ages (including all replicate ages).
    • Fig. S3. Average erosion rate curve from Fig. 4.
    • Fig. S4. Color bars showing lag intervals for all AHe cobble ages in our study, plotted separately for each deposit.
    • Fig. S5. Simplified version of Fig. 3.
    • Fig. S6. Age2edot output.
    • Fig. S7. Evolution of the closure depth in response to an instantaneous increase in erosion rate.

    Download PDF

    Other Supplementary Material for this manuscript includes the following:

    • Table S1 (Microsoft Excel format). Published bedrock ages shown in Fig. 3.
    • Table S2 (Microsoft Excel format). Crystal AHe measurements and ages.
    • Data S1. Google Earth file (.kml) of sample names and locations.

    Files in this Data Supplement:

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